Sure public bikes will do, but for me its kind of like the difference between my car and a bus. You have to wait for stations to become free a lot (usually commuting from my house to my work involved getting up half an hour before the crowds took the bikes). The bikes often have slight problems (loose breaks, squeaking, won't go into gear). Most people don't seem too bothered, but as somewhat of a bike enthusiast, I find it frustrating to know that its like just a spanner turn or two (end the bolts are usually non standard to prevent theft).

Its a great idea, but not without problems.